Method for production of a hybrid component

ABSTRACT

The invention relates to the production of a hybrid component, whereby a piece of metal sheet ( 1 ) is a least partly coated with plastic by injection molding, by means of the following steps: a) placing the metal sheet ( 1 ) in one mold half of an injection mold, b) closing the injection mold, such that a first mold cavity opposite an upper side (O) of the metal sheet ( 1 ) and a second mold cavity opposite an under side (U) of the metal sheet ( 1 ) are cut off from each other, c) treatment of the upper side (O) with plastic by means of at least a first sprue ( 9 ) to produce an essentially flat coating ( 4 ) connected to the metal sheet ( 1 ) and, finally, d) treatment of the under side (U) by means of at least one second sprue ( 10 ) to produce a reinforcing structure ( 6 ) connected to the metal sheet ( 1 ).

The invention relates to a method for production of a hybrid component,in which a piece of metal sheet is at least partly coated with plasticby injection molding.

According to the prior art, what are known as hybrid components arebeing increasingly used in automobile construction. These are pieces ofmetal sheet which are partly coated with plastic by theinjection-molding process. In this way, pieces of metal sheet can forexample be provided on their one side with a reinforcing structure. Ifsuitably designed, such hybrid components have greater rigidity; theyare also lightweight. Furthermore, hybrid components can be producedwith the accuracy known from the plastics injection-molding technique.Consequently, it is possible to mold complicated structures which cannotbe produced by means of the conventional metal sheet forming technique.

DE-A-26 09 084 discloses a hybrid chassis, comprising a metal plate withsynthetic resin supports. The mounting framework is arranged an aload-bearing framework for components in an electrical, electronic ormechanical device and comprises a carrying plate, which has at least onethrough-hole. Furthermore, the mounting framework comprises a syntheticresin support, which is integrally formed onto a first face of thecarrying plate. The synthetic resin support has a portion in which thethrough-hole of the carrying plate is set and via which it is integrallyconnected by a synthetic resin composition to the opposite face of thecarrying plate.

EP-B1-65 220 discloses a coated molded body with a metal plate, which isformed with a plurality of through-holes. The coated molded body hasresin parts which are connected by resin filled into the through-holesand protrude on the opposite sides of the metal plate, the resin partshaving a larger planar cross-sectional surface than that of thethrough-holes, and each resin part covering only one hole. A pluralityof resin bodies are disclosed, in each case formed in one piece with oneof the resin parts and kept independent of one another by the differencein the coefficient of thermal expansion between the resin parts and themetal plate. The coated molded body has, furthermore, resin parts notconnected by resin.

DE-C2-195 06 159 discloses an injection-molding process for molding aworkpiece with plastic. For this purpose, a mold with a mold cavity, aholding pin, an inlet for injecting the plastic into the mold cavity isused. The plastic is introduced into the mold cavity through a secondaryinlet. After the plastic in the mold cavity has cured, the mold isseparated and the plastic removed.

Hybrid components have nevertheless not yet been able to establishthemselves as body components in automobile construction. Onerequirement here is that the visible sides, i.e. the sides which arevisible in the fitted state, are also to be provided with a coatingproduced from the injection-molded plastic. This would make it possibleto dispense with painting the hybrid component. So far, successfulbonding of a defect-free coating with a small layer thickness to themetal sheet has not be accomplished.

The object of the invention is to overcome the disadvantages of theprior art. In particular, the intention is to provide a method by whicha hybrid component having a coating can be produced with satisfactoryquality.

A further aim of the invention is to produce the hybrid component asinexpensively and simply as possible.

According to the invention, a method for production of a hybridcomponent in which a piece of metal sheet is at least partly coated withplastic by injection molding is provided, comprising the followingsteps:

a) placing the piece of metal sheet into one mold half of an injectionmold

b) closing the injection mold, so that a first mold cavity, opposite anupper side of the piece of metal sheet, and a second mold cavity,opposite an underside of the piece of metal sheet, are cut off from eachother,

c) treatment of the upper side with plastic by means of at least onefirst sprue to produce an essentially flat coating connected to thepiece of metal sheet and, subsequently,

d) treatment of the underside with plastic by means of at least onesecond sprue to produce a reinforcing structure connected to the pieceof metal sheet.

Cutting off the first mold cavity and second mold cavity from each otherand the treatment of the upper side with plastic commencing earlier thanthe treatment of the underside with plastic achieve the advantage that athin-walled coating of satisfactory quality can be produced on the upperside of the piece of metal sheet. The reinforcing structure essentiallyperforms supporting, stiffening and retaining functions.

The piece of metal sheet is expediently treated with plastic in stepitem a in such a way that it neither changes its position nor isdeformed in step item d. A flow of plastic emerging from a first sprueis advantageously directed straight onto the upper face, i.e. the flowof plastic is not injected parallel to the upper side into the firstmold cavity. To prevent deforming of the metal sheet during spraying ofthe plastic onto the upper side, it is expedient to direct the flow ofplastic perpendicularly or at an obtuse angle onto the upper side.According to a further refining feature, the coating is sprayed on instep item c in a thickness of at most 3 mm. The thickness of the coatingmay vary. It depends in particular on the respective rheologicalconditions.

According to a further refining feature, the piece of metal sheet isheld in a clamping manner in the one mold half after placement,preferably by means of hydraulically movable holding means. Inparticular in the case of relatively small pieces of metal sheet, it isalso possible to hold them magnetically in the mold half. To ensurepositionally accurate placement, correspondingly formed fixed andmovable bearings are provided on the piece of metal sheet and in themold half. These may be formed on the mold as pins and on the piece ofmetal sheet as slots. According to a further refinement in terms of themethod, the piece of metal sheet is held in place—after closing of theinjection mold—in the injection mold by means of hold-down devicesformed onto the mold halves.

To connect the coating to the piece of metal sheet, first aperturesprovided on the piece of metal sheet are expediently injected through,so that anchoring elements produced in one piece with the coating areformed. To connect the reinforcing structure to the piece of metalsheet, second apertures provided on the piece of metal sheet areinjected through, so that second anchoring elements produced in onepiece with the reinforcing structure are formed. The hold-down devicesbearing against the upper side and underside are preferably coated insuch a way that the coating is not directly connected to the firstanchoring elements and/or the reinforcing structure is not directlyconnected to the second anchoring elements. The complete isolation ofthe coating from the reinforcing structure makes the production ofparticularly thin coatings possible.

According to a further refinement, the at least one hydraulicallymovable slide may be moved onto the upper side of the pieces of metalsheet before step item c to close a third aperture. The hydraulic slidemay be retracted before or during step item d, so that the thirdaperture is opened toward the second mold cavity and the cavity formedby the retraction of the hydraulic slide in the first mold cavity isfilled with plastic through said third aperture,—the aforementionedhydraulic slide is required in particular whenever complete separationof the coating from the reinforcing structure is not possible by meansof the hold-down devices for design reasons.

In particular for the production of large hybrid components, for examplefront masks for automobiles, it is advantageous that a number of piecesof metal sheet are placed into the mold in such a way that aperturesprovided in them are in line with one another. The plastic penetratesthrough the apertures, so that a connection is created between thepieces of metal sheet.

Furthermore, it is expedient that the pieces of metal sheet are coatedwith an anti-corrosion layer. The durability of the hybrid component isincreased as a result.

The first sprues are advantageously arranged outside a region of thecoating that is visible in the fitted state. A satisfactory visualquality of the visible side is ensured in this way.

Fourth mold cavities may be opened after the filling of the first moldcavity and/or second mold cavity, and further plastic injected into saidfourth mold cavities. The further plastic may be a plastic withdifferent properties, for example a different color or a differentelasticity. For example, after the spraying of the coating, a fourthcavity may be opened and a seal formed from elastic plastic sprayed ontothe coating.

An exemplary embodiment of the method according to the invention isexplained in more detail below on the basis of the drawings, in which:

FIG. 1 shows a schematic cross-sectional view through a metal sheetbefore the first injection-molding operation,

FIG. 2 shows the metal sheet according to, FIG. 1 after the firstinjection-molding operation,

FIG. 3 shows the metal sheet according to FIG. 2 after the secondinjection-molding operation,

FIG. 4 shows a plan view of a hybrid component and

FIG. 5 shows a schematic cross-sectional view of a further hybridcomponent.

In FIG. 1, a piece of metal sheet 1 is shown schematically in crosssection. The piece of metal sheet 1 is provided with first apertures 2and with second apertures 3. An upper side is denoted by O and anunderside by U. The piece of metal sheet 1 is coated with ananti-corrosion layer (not shown here).

FIG. 2, a coating 4 has been sprayed onto the piece of metal sheet 1.First rivet-like anchoring elements 5 reach through the first apertures2 and form thickenings on the underside U of the piece of metal sheet 1.

In FIG. 3, the situation after the injection-molding of a reinforcingstructure 6 onto the underside U is shown. The reinforcing structure 6has ribs 7 running essentially perpendicularly in relation to theunderside. On the reinforcing structure 6, further rivet-like anchoringelements 8 extend through the second apertures 3 and have on the upperside O of the piece of metal sheet 1 further thickenings. As can beclearly seen from FIG. 3, there is no direct connection between thecoating 4 and the reinforcing structure 6, i.e. no material bridge whichis formed from plastic.

In figure 4, the piece of metal sheet 1 is shown in plan view. A visibleregion of the coating 4 is rectangularly formed. From the visible regionthere extends a tongue-like projection. Located here is a first sprue 9,which is formed by a heated first nozzle (not shown here). It goeswithout saying that, depending on the size of the coating formed, anumber of first sprues may also be provided. The jet emerging from thefirst nozzle impinges essentially perpendicularly onto the upper side Oof the piece of metal sheet 1. Second sprues 10 are formed as what areknown as hot/cold runners. The jet of plastic emerging from secondnozzles (not shown here) passes via the hot/cold runners to a secondmold cavity, enclosing the reinforcing structure 6.

For production of a hybrid component according to the invention, thepiece of metal sheet 1 is initially placed into a mold half (not shownhere) of an injection mold. For the exact positioning of the piece ofmetal sheet, fixed and movable bearings are provided, for example in theform of pins provided on the one mold half and slots on the piece ofmetal sheet, which engage in one another when the piece of metal sheetis put in place. In order to hold the piece of metal sheet in the moldhalf, holding means attached to the one mold half are subsequently movedhydraulically onto the piece of metal sheet in such a way that it isheld in a clamping manner. The injection mold is closed. The piece ofmetal sheet is then additionally held in a clamping manner in theinjection mold by means of hold-down devices attached to the moldhalves. A first mold cavity, enclosing the coating, is cut off from asecond mold cavity, enclosing the reinforcing structure 6. Plastic isthen injected directly onto the surface O of the piece of metal sheetvia the first sprue, which is formed here as a “hot runner”.

Subsequently, expediently 0.3–0.8 seconds after the firstinjection-molding operation, plastic is injected into the second moldcavity via the second sprues 10. The first mold cavity is filled withplastic earlier than the second mold cavity. This avoids the piece ofmetal sheet 1 being deformed or changing its position. It has proven tobe particularly advantageous to direct the flow of plastic emerging fromthe hot runner into the first mold cavity directly onto the upper side Oof the piece of metal sheet 1, to be precise expediently at an obtuseangle. By contrast, the reinforcing structure 6 is injection-moldedconventionally via hot/cold runners.

For design reasons, it may be that the first apertures 2 and the secondapertures 3 are to be placed in such a way that a material bridge isformed in the completed hybrid component between the coating 4 and thereinforcing structure 6. For this purpose—as can be seen from FIG.5—after closing of the mold, hydraulic slides 11 are moved onto theupper side O in such a way that third apertures 12 are closed as aresult. This state is shown on the left in FIG. 5. Then, as mentionedabove, the coating 4 is sprayed via the hot runner 9 directed directlyonto the upper side O. The plastic flows around the hydraulic slides 11.Subsequently or after the spraying of the coating 4, the hydraulicslides 11 are retracted. Plastic passes from the second mold cavitythrough the third apertures 12 into the first mold cavity, surroundingthe coating 4. The cavities formed by the hydraulic slides 11 in theretracted state are filled.

Polyamide with added short glass fibers or polypropylene with long glassfibers is expediently used as the plastic. It goes without saying thatany other injection-moldable plastic may also be used.

The method according to the invention is suitable in particular forproduction of highly integrated hybrid components for automobileconstruction. For example, a front mask for a motor vehicle can beproduced quickly and at low cost. It is possible to mold seals for theradiator hood on the upper side of the front mask by means of themulti-component technique known per se. The reinforcing structure mayhave, for example, the mounting for a ventilation motor. Furthermore,elastic receptacle of a one-piece form may be provided for the radiator.Retaining lugs for cable or cable harnesses could be a component part ofthe reinforcing structure.

1. A method for production of a hybrid component, in which a piece ofmetal sheet (1) is at least partly coated with plastic by injectionmolding, comprising the following steps: a) placing the piece of metalsheet (1) in one mold half of an injection mold, b) closing theinjection mold, so that a first mold cavity, opposite an upper side (O)of the piece of metal sheet (1), and a second mold cavity, opposite anunderside (U) of the piece of metal sheet (1), are cut off from eachother, c) treating the upper side (O) with plastic by means of at leastone first sprue (9) to produce an essentially flat coating (4) connectedto the piece of metal sheet (1) and, subsequently, d) treating theunderside (U) with plastic by means of at least one second sprue (10) toproduce a reinforcing structure (6) connected to the piece of metalsheet (1).
 2. The method as claimed in claim 1, wherein the piece ofmetal sheet (1) is treated with plastic in step c in such a way that itneither changes its position nor is deformed in step d.
 3. The method asclaimed in claim 1, wherein a flow of plastic emerging from a firstsprue is directed onto the upper side (O).
 4. The method as claimed inclaim 1, wherein the flow of plastic is directed perpendicularly or atan obtuse angle onto the upper side (O).
 5. The method as claimed inclaim 1, wherein the coating (4) is injected or sprayed on in step c ina thickness of at most 3 mm.
 6. The method as claimed in claim 1,wherein the piece of metal sheet is held in a clamping manner in the onemold half after placement.
 7. The method as claimed in claim 1, whereinthe piece of metal sheet (1) is held in place after closing of theinjection mold by means of hold-down devices formed onto the holdhalves.
 8. The method as claimed in claim 1, wherein first apertures (2)provided on the piece of metal sheet (1) is injected through to connectthe coating (4), so that first anchoring elements (5) and the coating(4) are formed in one piece.
 9. The method as claimed in claim 8,wherein second apertures (3) provided on the piece of metal sheet (1)are injected through to connect the reinforcing structure (6), so thatsecond anchoring elements (8) and the reinforcing structure (6) areformed in one piece.
 10. The method as claimed in claim 9, whereinhold-down devices bearing against the upper side (O) and underside (U)are coated, so that the coating (4) is not directly connected to thesecond anchoring elements (8) and/or the reinforcing structure (6) isnot directly connected to the first anchoring elements (5).
 11. Themethod as claimed in claim 9, wherein at least one hydraulically movableslide (11) is moved onto the upper side (O) of the piece of metal sheet(1) before step c to close a third aperture (12).
 12. The method asclaimed in claim 11, wherein the hydraulic slide (11) is retractedbefore or during step d, so that the third aperture (12) is openedtoward the second mold cavity and the cavity formed by the retraction ofthe hydraulic slide (11) in the first mold cavity is filled with plasticthrough said third aperture.
 13. The method as claimed in claim 8,wherein a number of pieces of metal sheet (1) are placed in theinjection mold in such a way that apertures provided in them are in linewith one another.
 14. The method as claimed in claim 1, wherein thepieces of metal sheet (1) are coated with an anti-corrosion layer. 15.The method as claimed in claim 1, wherein the first sprue (9) isarranged outside a region of the coating (4) that is visible in thefitted state.
 16. The method as claimed in claim 1, wherein fourth moldcavities are opened after the filling of the first mold cavity and/orsecond mold cavity, and further plastic being injected into said fourthmold cavities.